The control of hindgut motility in the lobsterHomarus gammarus(L.)

Abstract

1. The structure of the sixth abdominal ganglion (6 A.G.) of Homarus has been determined using light microscopy. The ganglionic cortex is divided into anterior and posterior ventral lobes. A pair of dorsal lobes arises from the posterior ventral lobe. Four pairs of commissures cross the ganglion and six pairs of nerves arise from it. 2. The 6 A.G. is suggested to have been derived from three fused ganglia ‐ the sixth and seventh abdominal ganglia and a terminal ganglion. Evidence is presented to support this hypothesis. 3. Lesion and ablation experiments were carried out on the 6 A.G. Motor activity from the posterior intestinal nerves (P.I.N.’s) is elicited by the activity of at least two pairs of interneurones (I1 and I2) which decussate in the 6 A.G. The somata of neurones controlling the defaecatory response are located in the anterior region of the posterior ventral lobe. 4. Cells producing unitary and bursting motor discharge down the P.I.N.’s were penetrated using glass microelectrodes. Three types of neurones are thought to be located in the hindgut control network at the level of the 6 A.G. These are unitary and bursting motor neurones and driver interneurones. 5. Our present knowledge of the hindgut control system of Homarus is summarised and compared with the system in the cockroach, Periplaneta americana.